A Cost-Effective Winding Structure On Modular Matrix Transformer LLC Application

Modular transformer structure LLC resonant converter with PCB winding achieves high conversion ratio and power density while minimizing winding loss and ensuring current sharing. However, the large inter-winding capacitance not only results in severe electromagnetic interference issue, but also forms a multi element resonant tank instead of LLC which causes additional winding loss from higher order harmonics. In this paper, an analytical model is first derived to illustrate inter-winding capacitance which is non-trivial from efficiency point of view. Then a cost-effective winding structure with smaller inter-winding capacitance and similar ac resistance is implemented without increasing the size of the transformer. The experiment results show the proposed winding structure in three-transformer (3M) structure improves 0.3% efficiency improvement at heavy load compared to the conventional PCB windings in 3M structure LLC converter.